The tubes are usually sealed at their respective ends to be joined by a squeeze weld seam extending transversely to the tube axis. The tube ends are inserted in aligned position along a common axis in two mounting blocks which are movable relative to each other. By means of a heating unit movable between the mounting blocks, the facing ends are melted. After removing the heating unit, the tube ends are pressed against each other in axial direction.
From the European patent No. EP-A2 No. 00 44 204, such an apparatus and process is known. The plastic tubes are inserted in overlapping manner in the respective mounting blocks. The heating unit is of the electrically heated blade type which is moved between the mounting blocks and cuts off both exposed overlapping tube sections with their respective weld seam while sealing the molten interface between the facing tube ends. The fusing contact is maintained even after subsequent relative movement of the mounting blocks which align the tube ends to be joined along a common axis.
Several drawbacks are encountered with this apparatus and method. Since each docking and splicing operation requires a preceding cutting of certain tube sections, considerable amount of waste accumulates which is undesirable from an economical standpoint, and which severely limits the number of possible joining processes depending on the length of the tube. In view of the unavoidable relative movements between the fused interfaces and the heated blade in the joining area, plastic beads are encountered which will increase the flow resistance. Further, the sealing of the tube ends may be disrupted during retraction of the heating unit so that contamination can penetrate into the tube. To maintain sterility of the process, it is necessary to exchange the blades prior to each docking because residues of plastic material stick to the heated blades.
Apart from these drawbacks, the apparatus according to No. EP-A2 No. 00 44 204 requires also complicated guiding means as the mounting blocks are not only moved in transverse direction relative to the heating unit and relative to each other in longitudinal direction but also in transverse direction relative to each other.
U.S. Pat. No. 3,968,195 discloses a method for making sterile connections between two tubelike blood bags. Before docking, the tube is closed off by clamps at a distance to the free ends of the aligned tubes. A Bunsen burner is used to apply heat to the free tube ends which are softened and then brought into contact. After holding the tube end in this position and allowing them to cool and to solidify, a permanent connection is formed.
This has the disadvantage, however, that the tube end sections must be designed in a special and complicated manner. As disclosed therein, in the tube end, a rigid tube is inserted whose free end is sealed off by a thin thermoplastic diaphragm.